The present invention is directed to an apparatus and method useful in thermally treating glass sheets or panels for tempering, annealing and/or shaping of the glass which can include quenching to remove heat. The shaping of the glass can involve bending glass sheets, placing curves in glass sheets and otherwise changing the contour of glass sheets and panels, such as in bending float glass sheets. Also the invention is directed to the resultant thermally treated glass sheets.
Glass sheets, panes, panels or parts have been heated for tempering, for annealing and for shaping as in bending, or placing curves or contours in the glass in industry by use of various processes and accompanying apparatus. Conventional tempering and annealing processes involve heating the glass with subsequent cooling of the heated glass at particular rates while the glass is supported on support members such as rings or outline molds. Shaping processes for glass include gravity bending, press bending, roll bending and like processes. These are as opposed to any production of glass bottles through blowing. In these glass shaping methods the heated glass is at a temperature for non-breaking deformation so that the glass accepts a shape or curve or bend given through one or more supporting and/or contacting members acting as a mold.
For instance, in gravity bending, bending fixtures or irons carry the glass through a furnace or a lehr to support the glass sheet during heating and usually also during subsequent cooling. The fixture usually supports the underside or bottom surface of the glass sheet in such a manner to allow for its bending or sagging due to gravity. The outlying shaping rail of the fixture provides the support and also can have an upper surface with elevational contours corresponding to at least part of the final desired shape of the glass sheet. With bending irons the main area of the glass is usually untouched during the bending process since the support is along the marginal end of the one or more glass sheets. The heated glass at its heat softening temperature sags by gravity to adopt the desired configuration. Also, bending irons can have movable parts to assist in the shaping of the glass. The shaping rails themselves can be segmented and/or made to pivot from an open, rigid sheet supporting position to a closed, heat-softened glass sheet supporting position for more difficult or complex bends or curves for the shaped glass. Such a technique is suitable for simultaneous shaping of two sheets of glass or doublet that will be used as the inner and outer plies of conventional laminated glass such as a windshield. For instance, automotive windshields can be made by placing one or more flat glass sheets on the support surface of the bending iron with appropriate spacing material for doublet sheets as that available in U.S. Pat. No. 6,076,373 (Grodziski); U.S. Pat. No. 4,066,429 (Reese et al.); U.S. Pat. No. 3,880,636 (Tobeman et al.); U.S. Pat. No. 6,006,549 (Safka et al.). These are all incorporated herein by reference.
As the glass sags or bends due to gravity the glass contacts an increasing surface of the shaping rails along the bottom marginal edge of the glass. This increasing contact is as opposed to the fewer contact points for the cold precut single or multiple glass sheets placed on the rigid non-articulating or articulating metal shaping rails of the bending iron. The rails themselves are usually pre-shaped to have a shape to support the unbent sheet while also supplying the mold for the curved or bent sheets. The contact of the glass with the rail in bending can give rise to infrequent slight surface markings along the periphery of the bent glass sheet. In addition to these types of scuff markings, other markings on the glass can occur from indentations occurring from inappropriate time and/or temperature experienced by the heated glass on the irons. Other markings can arise from transfer defects on the irons themselves; such as burrs of glass deposited on the rail from previous glass sheets that were shaped. Such surface markings can be accommodated for in laminated windshield products by concealing and glazing or framing parts for the bent glass.
Additionally, shaped glass can be produced from pressure forming which is usually the process used for making curved automotive side windows and back windows although gravity forming equipment could also be used. In the pressure forming of glass sheets pressurized gas assists in shaping the heat-softened glass sheet(s). The glass sheet first can be pre-shaped; for instance by sagging by gravity bending onto a ring or outline mold in a support frame. The mold with the glass and an upper mold of a molding device are moved relative to each other. This movement is to position the molds either in close proximity to each other or to press the upper mold itself against the heated glass. Hot air issues either selectively or more uniformly from the upper mold to flow towards the glass surface. A useful pressure forming process is shown in U.S. Pat. No. 5,669,952 (Claassen et al.). In this patent the mold includes a rail member having a support surface that generally conforms to the elevation and outline of the final longitudinal and transverse shape desired for the bent glass sheets. The rail member itself may be a bar member that supports the glass sheets slightly inboard of the glass sheets periphery or it may be an xe2x80x9cLxe2x80x9d or xe2x80x9cTxe2x80x9d shaped member. In pressure forming similar markings can occur on the shaped glass similar to those that can occur in gravity bending.
Additionally, with gravity and press bending, cooling of the shaped glass sheets usually occurs through natural convection or low level forced air cooling.
It is an object of the present invention to provide an apparatus and method and the resulting thermally treated glass having reduced bottom surface defects in particular reduced surface marks which can result when glass is tempered, annealed, shaped or bent on support apparatus or equipment.
The invention relates to an apparatus and method useful in the thermal treatment of glass sheets or panels and the resulting treated glass sheets and panels. The apparatus is capable of supporting the glass during thermal treatment such as tempering, annealing, bending, and/or shaping which can include any cooling or quenching to remove heat or any combination of these. In one aspect of the invention the apparatus useful for thermal treatments such as tempering and annealing, including the cooling step, is a ring or outline mold. The ring has a horizontal surface suitable for contacting the glass. The horizontal surface can be configured so that it is not just horizontal but may be somewhat non-planar to have an elevational configuration for certain portions or segments. For heat treatments for bending or shaping the apparatus of the present invention can have a support frame and one or more support members attached to the support frame. The support members like the horizontal surface of the ring can conform in elevation, outline or contour, and shape to provide support to one or more glass sheets or panels during thermal treatment. Also the support members can provide support during cooling.
At least the surface of the ring and the support members with or without a coating for contact with the glass are of one or more metals having a thermal conductivity such that the glass heated for shaping cools at a rate not much slower than the cooling rate of unsupported sections of the glass. For instance suitable metals include those with a thermal conductivity of greater than around 60 BTU/(hourxc3x97feetxc3x97xc2x0 F. so that the shaped glass can have the requisite edge stress levels desired. In the units above, xe2x80x9cxxe2x80x9d indicates multiplication. The shape and dimensions of the ring and the support member provide the necessary rigidity to support the glass. These parameters and this characteristic are balanced with the thermal characteristics of the metal for the ring and the support member so that the ring and the support member do not adversely retard the cooling of the glass surface. The shape and/or dimensions of the ring and the support member for certain metals could result in the ring or support member cooling at a slower rate than the glass. Both the ring and support member have designs, shapes, and/or dimensions that for the particular metal or metals of the ring or support member can result in the ring or support member cooling at the same or faster rate than the glass which it supports.
Suitable aforementioned support frames include the non-articulating and articulating types of bending irons and frames known in the art. The articulating irons can add shaping by any method or features known to those skilled in the art. For such bending irons the support members of the inventions would be the shaping rail. Generally the bending irons function as molds for shaping heat softened sheets, e.g., glass sheets. The bending mold has a central portion and can have one or more articulating pivoting end sections. Force applying facilities, e.g., weight assemblies, pressurized canisters, springs or the like can be mounted on the sides of the mold usually in proximity to the outer side of the associated end section of the bending mold. The supporting member or shaping rail can have a shape to support the glass before and during and usually after sagging and bending operations from heat and any mechanical forces. Generally the cross-sectional shape of the supporting member can be xe2x80x9cL-shapedxe2x80x9d, xe2x80x9cT-shapedxe2x80x9d, rectangular, triangular or any nearly flat shape or the like to provide a supporting surface for the glass at or near the marginal edge of the supported surface, usually the bottom surface, of the glass. The support member can have any suitable attachment to the supporting frame.
The present invention also relates to a method of thermally treating and/or a method of shaping one or more sheets, e.g., glass sheet, using a ring or mold, like an outline mold, embodying features of the invention. Such thermal treatment method can include the cooling or quenching of heated glass. The heating method involves placing the glass panels for heat treatment such as tempering or annealing on a ring as a support member such as a tempering or annealing ring so that the glass is supported at or around at least its marginal surface at enough locations on the frame to adequately hold the glass. When the thermal treatment method involves bending or shaping, the glass sheets, panel or panels with preliminary dimensions are placed on the support members of the molding frame for at least marginal support to adequately hold the glass during one or all of heating, shaping and cooling. Both molding frame and supported glass can be heated to a temperature to facilitate the bending or sagging of the glass panel or panels. As the glass bends or sags, the glass may contact more of the supporting members"" or rail""s surface adequate for the supporting member to function as a mold for the shape of the bent glass sheet or panel around at least the marginal edge of the glass sheet. After the glass bends or sags to shape the molding frame and glass are removed from the heat for cooling of the shaped glass. In the described methods the ring and support member have the surface that with or without a coating contacts the glass made of one or more of the metals having a thermal conductivity of at least around 16 BTU/(hourxc3x97feetxc3x97xc2x0 F.).
Additional aspects of the present invention include the shaped glass, various support configurations, and optional coating for the supports or rings. The shaped glass has fewer mold marks on its surface from contacting the supporting members than glass undergoing heat treatment with traditional supporting structures. The support member or ring or mold can have various shape configurations to hold the glass sheet or sheets, and can have a heat resistant and/or anti-corrosive and/or abrasion resistant coating to improve durability.